Recently, display devices such as liquid crystal display devices, typified by, for example, a liquid crystal display television and a liquid crystal display monitor, have adopted a backlight device as a light emitting device for emitting light from the back, side or the like of a display panel. As the backlight device, what is called an edge-lighting (a side-lighting) type exists in which alight source is disposed on two or one side of a light guide plate made of transparent resin so that light incident on the light guide plate is reflected by a reflector disposed on the back surface of the light guide plate, thus illuminating the surface of a liquid crystal display panel.
A fluorescent tube such as a hot-cathode fluorescent tube or a cold-cathode fluorescent tube is generally used as the above-mentioned backlight device. On the other hand, technologies of backlight devices using light emitting diodes (LEDs), which are one type of solid-state light emitting elements, as a light source, have been recently developed as a substitute for the backlight devices using the fluorescent tubes. A backlight device with light sources arranged on a side of a light guide plate has been known as a back light device of the side-light type using light emitting diodes (for example, refer to Patent Document 1). The light sources are formed of a substrate on which plural light emitting diodes are mounted.    Patent Document 1: Japanese Patent Application Laid Open Publication No. 6-3527